Even though the amount of plastics, hereinafter polymers, used in a variety of consumer goods, packaging, and medical articles has not significantly increased over the past twenty years, the common perception is that more and more non-degradable plastics are filling up our limited landfill space. Despite this perceived disadvantage, polymers continue to be used in the manufacture of consumer goods, packaging and medical articles because plastics offer many advantages over the more traditional materials: wood, glass, paper, and metal. The advantages of using polymers include decreased manufacturing time and costs, improved mechanical and chemical properties, and decreased weight and transportation costs. It is the improved chemical resistance properties of the majority of plastics that result in their non-degradability.
Disposal of waste materials, including food waste, packaging materials and medical waste, into a typical landfill provides a relatively stable environment in which none of these materials is seen to decompose at an appreciable rate. Alternative waste disposal options have been increasingly discussed and utilized to divert some fractions of waste from entombment. Examples of these alternatives include municipal solid waste composting, anaerobic digestion, enzymatic digestion, and waste water sewage treatment.
Much controversy is associated with the disposal of medical waste. Both government agencies and members of the private sector have been increasingly directing in-depth scrutiny and funds toward this subject. Admittedly, concerns over the fate of materials contaminated with infectious substances are valid and proper measures to insure the safety of health care workers and the general public should be taken.
Currently, medical waste can be categorized as either reusable or disposable. Categorization as to whether certain waste is reusable or disposable is customarily determined according to the material from which the article was constructed and the purpose for which the article was used.
After use, reusable medical articles are cleansed and sterilized under stringent conditions to ensure disinfection. In comparison, disposable medical articles are usually only used once. Even then, disposing procedures are not straightforward, rather they often involve several steps to safeguard against potential hazards. Typically, after use, disposable medical articles must be disinfected or sterilized, adding a significant cost prior to disposal into a specially designated landfill or waste incinerator. As a result, the disposal cost for the contaminated single use articles is quite high.
Despite the high cost of disposal, single use medical articles are desirable because of the assurance of clean, and uncontaminated equipment. Many times in the medical context, sterilization procedures conducted improperly can result in detrimental effects, such as the transmission of infectious agents from one patient to another. Improper sterilization can also be disastrous in a laboratory setting, where, for example, contaminated equipment can ruin experiments resulting in tremendous costs of time and money.
Currently, disposable medical fabrics are generally composed of thermoplastic fibers, such as polyethylene, polypropylene, polyesters, polyamides and acrylics. These fabrics can also include mixtures of thermoset fibers, such as polyamides, polyarimides and cellulosics. They are typically 10-100 grams per square yard in weight and can be woven, knitted or otherwise formed by methods well known to those in the textile arts while the non-wovens can be thermobonded, hydroentangled, wet laid or needle punched and films can be formed by blown or cast extrusion or by solution casting. Once used, these fabrics are difficult and costly to dispose of and are non-degradable.
The use of polymers for various disposable articles is widespread and well known in the art. In fact, the heaviest use of polymers in the form of films and fibers occurs in the packaging and the disposable article industries. Films employed in the packaging industry include those used in food and non-food packaging, merchandise bags and trash bags. In the disposable article industry, the general uses of polymers occurs in the construction of diapers, personal hygiene articles, surgical drapes and hospital gowns, instrument pads, bandages, and protective covers for various articles.
In light of depleting landfill space and inadequate disposal sites, there is a need for polymers that are water-responsive. Currently, although polymers, such as polyethylene, polypropylene, polyethylene terephthalate, nylon, polystyrene, polyvinyl chloride and polyvinylidene chloride, are popular for their superior extrusion and film and fiber making properties, these polymers are not water-responsive. Furthermore, these polymers are generally non-compostable, which is undesirable from an environmental perspective.
Polymers and polymer blends have been developed which are generally considered to be water-responsive. These are polymers which purportedly have adequate properties to permit them to breakdown when exposed to conditions which lead to composting. Examples of such arguably water-responsive polymers include those made from starch biopolymers and polyvinyl alcohol.
Although materials made from these polymers have been employed in film and fiber-containing articles, many problems have been encountered with their use. Often the polymers and articles made from these polymers are not completely water-responsive or compostable. Furthermore, some water-responsive polymers may also be unduly sensitive to water, either limiting the use of the polymer or requiring some type of surface treatment to the polymer, often rendering the polymer non-water-responsive. Other polymers are undesirable because they have inadequate heat resistance for wide spread use.
Personal care products, such as diapers, sanitary napkins, adult incontinence garments, and the like are generally constructed from a number of different components and materials. Such articles usually have some component, usually the backing layer, constructed of a liquid repellent or water-barrier polymer material. The water-barrier material commonly used includes polymer materials, such as polyethylene film or copolymers of ethylene and other polar and non-polar monomers. The purpose of the water-barrier layer is to minimize or prevent absorbed liquid that may, during use, exude from the absorbent component and soil the user or adjacent clothing. The water-barrier layer also has the advantage of allowing greater utilization of the absorbent capacity of the product.
Although such products are relatively inexpensive, sanitary and easy to use, disposal of a soiled product is not without its problems. Typically, the soiled products are disposed in a solid waste receptacle. This adds to solid waste disposal accumulation and costs and presents health risks to persons who may come in contact with the soiled product. An ideal disposal alternative would be to use municipal sewage treatment and private residential septic systems by flushing the soiled product in a toilet. Products suited for disposal in sewage systems are termed “flushable”. While flushing such articles would be convenient, prior art materials do not disintegrate in water. This tends to plug toilets and sewer pipes, frequently necessitating a visit from a plumber. At a municipal sewage treatment plant, the liquid repellent material may disrupt operations by plugging screens and causing sewage disposal problems. In such prior art products, it is therefore necessary, although undesirable, to separate the barrier film material from the absorbent article prior to flushing.
In addition to the article itself, typically the packaging in which the disposable article is distributed is also made from a water-barrier, specifically water-resistant, material. Water-resistivity is necessary to prevent the degradation of the packaging from environmental conditions and to protect the disposable articles therein. Although this packaging may be safely stored with other refuse for commercial disposal, and especially in the case of individual packaging of the products, it would be more convenient to dispose of the packaging in the toilet with the discarded, disposable article. However, where such packaging is composed of a water-resistant material, the aforementioned problems persist.
The use of lactic acid and lactide to manufacture a water-stable polymer is well known in the medical industry. Such polymers have been used in the past for making water-stable sutures, clamps, bone plates and biologically active controlled release devices. Processes developed for the manufacture of such polymers to be utilized in the medical industry have incorporated techniques which respond to the need for high purity and biocompatibility in the final product. These processes, however, are typically designed to produce small volumes of high dollar-value products, with less emphasis on manufacturing cost and yield.
It is generally known that lactide polymers or poly(lactides) are unstable. However, the consequence of this instability has several aspects. One aspect is the biodegradation or other forms of degradation which occur when lactide polymers, or articles manufactured from lactide polymers, are discarded or composted after completing their useful life. Another aspect of such instability is the degradation of lactide polymers during processing at elevated temperatures as, for example, during melt processing by end-user purchasers of polymer resins.
In the medical area, there is a predominant need for polymers which are highly stable and therefore desirable for use in medical devices. Such a demand has historically been prevalent in the high value, low volume medical specialty market, but is now also equally prevalent in the low value, high volume medical market.
As described in U.S. Pat. No. 5,472,518, compositions comprised of multi-layer polymer films are known in the art. The utility of such structures lies in the manipulation of physical properties in order to increase the stability or lifetime during use of such structure. For example, U.S. Pat. No. 4,826,493 describes the use of a thin layer of hydroxybutyrate polymer as a component of a multi-layer structure as a barrier film for diaper components and ostomy bags.
Another example of use of multi-layer films is found in U.S. Pat. No. 4,620,999 which describes the use of a water-soluble film coated with, or laminated to, a water insoluble film as a disposable bag. The patent describes a package for body waste which is stable to human waste during use, but which can be made to degrade in the toilet, at a rate suitable for entry into a sewage system without blockage, by adding a caustic substance to achieve a pH level of at least 12. Such structures usually consist of a polyvinyl alcohol film layer coated with polyhydroxybutyrate.
A similar excretion-treating bag allowing discarding in flush toilet or sludge vessel is disclosed in JP 61-42127. It is composed of an inner layer of a water-resistant polymer, such as polylactide, and an outer layer of a water-dispersible polymer, such as polyvinyl alcohol. As disclosed in this patent, there are many examples of multi-layer films that are utilized in disposable objects. Most of these examples consist of films or fibers which are comprised of internal layers of an environmentally degradable polymer and an external layer of water-responsive polymer. Typically, the internal layers are comprised of polycaprolactone or ethylene vinyl acetate and the external layer is comprised of polyvinyl alcohol. These examples, however, are all limited to compositions consisting of multi-layer of different polymers, and do not encompass actual blends of different polymers.
A family of patents, EP 241178, JP 62-223112 and U.S. Pat. No. 4,933,182, describes a controlled release composition for treating periodontal disease. The controlled release compositions are comprised of a therapeutically effective agent in a carrier consisting of particles of a polymer of limited water solubility dispersed in a water-soluble polymer. Although, the carrier of these inventions includes the use of more than one polymer, the disclosed carrier is not a blend because the polymer of limited water solubility is incorporated in the water-soluble polymer as particles ranging in average particle size from 1 to 500 microns.
The use of polymers for use in water-responsive articles is disclosed in U.S. Pat. Nos. 5,508,101; 5,567,510; and 5,472,518. This group of patents discloses a series of water-responsive compositions comprising a hydrolytically degradable polymer and a water-soluble polymer. The compositions of this group, however, consist of articles constructed from polymers which are first formed into fibers or films and then combined. As such, the compositions are actually mini-layers of the individual polymer films or fibers. Therefore, although the fibers and films of the polymers of such compositions are considered to be in very close proximity with one another, they are not as intimate as actual polymer blends. The dispersion of one polymer within another in these compositions is not viewed as approximately uniform since the individual polymers are essentially distinct and separate fibers or films.
U.S. Pat. No. 5,525,671 to Ebato et al. discloses a method of making a linear lactide copolymer from a lactide monomer and a hydroxyl group containing monomer. The polymer disclosed by Ebato is a linear lactide copolymer produced by reacting two monomers to form a linear polymer with a block or random structure. Ebato does not disclose graft copolymers.
Polymer blend compositions for making fibers and films that are optimally combined are desirable because they are highly stable. Optimal combination of polymers means that the polymers are connected as closely as possible without the requirement of co-polymerization. Although physically blended individual polymer compositions are known, improved polymer blends within the fibers and films the individual fibers are microscopically intimately interfaced are desirable since the resulting composition is then more stable, pliable and versatile and most importantly having improved properties and performance.
In addition to the need for polymer compositions that are highly stable, and, therefore, suitable for regular use in most disposable articles, there is a simultaneous need for such polymer compositions to be water-responsive. What is needed therefore, is a material that may be utilized for the manufacture of disposable articles and which is water-responsive. Such material should be versatile and inexpensive to produce. The material should be stable enough for intended use but subject to degradation under predetermined conditions during disposal.
Moreover, there is an increased emphasis on environmentally safe materials and coatings. These coatings reduce the use of solvent-based coatings and rely, to an ever-increasing degree, on polar coatings, such as water-based material. The utility of the graft copolymers of this invention includes, but would not be limited to, materials having a greater affinity for a polar coating.
Therefore, it is an object of this invention to provide a modified, hydrolytically biodegradable polymer.
Another object of this invention is to provide a thermally processable polymer.
Another object of this invention is to provide a commercially viable polymer.
A further object of this invention is to provide a thermally processable, biodegradable polymer which is more compatible with polar polymers and other polar substrates or components.
Still another object of this invention is to provide a modified, hydrolytically biodegradable polymer useful for making flushable, biodegradable articles.
Yet another object of this invention is to provide a modified, hydrolytically biodegradable polymer useful for making blends with improved mechanical and physical properties.
Another object of this invention is to provide a modified biodegradable polymer with improved melt processability.
A further object of this invention is to provide a polymer blend of unique microstructure.
Another object of this invention is to provide a modified biodegradable polymer which has improved compatibility in blends with polar polymers.
Another object of the invention is to provide improved polymer blends comprising poly(β-hydroxybutyrate-co-valerate), poly(butylene succinate) and/or polycaprolactone.